Effects of acute ingestion of a pre-workout dietary ...alpha-ketoglutarate [9] as well as other nutrients pur-ported to effect cognitive function like tyrosine [10, 11] and Mucuna

RESEARCH ARTICLE Open Access

Effects of acute ingestion of a pre-workoutdietary supplement with and withoutp-synephrine on resting energyexpenditure, cognitive function andexercise performanceY. Peter Jung1, Conrad P. Earnest1,2, Majid Koozehchian1, Elfego Galvan1, Ryan Dalton1, Dillon Walker3,Christopher Rasmussen1, Peter S. Murano4, Mike Greenwood1 and Richard B. Kreider1*

Abstract

Background: The purpose of this study was to examine the effects of acute ingestion of a pre-workout dietarysupplement (PWS) with and without p-synephrine (S) on perceptions of readiness to perform, cognitive function,exercise performance, and markers of safety.

Methods: In a randomized, double-blind, and counterbalanced manner; 25 healthy and recreationally active maleand female participants ingested a flavored maltodextrin placebo (PLA), a PWS containing beta-alanine (3 g),creatine nitrate as a salt (2 g), arginine alpha-ketoglutarate (2 g), N-Acetyl-L-Tyrosine (300 mg), caffeine (284 mg),Mucuna pruiriens extract standardized for 15% L-Dopa (15 mg), Vitamin C as Ascorbic Acid (500 mg), niacin (60 mg),folate as folic acid (50 mg), and Vitamin B12 as Methylcobalamin (70 mg) with 2 g of maltodextrin and flavoring; or,the PWS with Citrus aurantium (PWS + S) extract standardized for 30% p-synephrine (20 mg). Participants had heartrate (HR), blood pressure, resting energy expenditure (REE), 12-lead electrocardiograms (ECG), perceptions aboutreadiness to perform, cognitive function (Stroop Color-Word test), bench and leg press performance (2 sets of 10repetitions at 70% of 1RM and 1 set to failure), and Wingate anaerobic capacity (WAC) sprint performancedetermined as well as donated blood samples prior to and/or following exercise/supplementation. Data wereanalyzed by MANOVA with repeated measures as well as mean changes from baseline with 95% confidenceintervals (CI).

Results: No clinically significant differences were observed among treatments in HR, blood pressure, ECG, orgeneral clinical blood panels. There was evidence that PWS and PWS + S ingestion promoted greater changes inREE responses. Participants reported higher perception of optimism about performance and vigor and energy withPWS and PWS + S ingestion and there was evidence that PWS and PWS + S improved changes in cognitive functionscores from baseline to a greater degree than PLA after 1 or 2 h. However, the scores in the PWS + S treatment didnot exceed PLA or PWS responses at any data point. No statistically significant differences were observed amongtreatments in total bench press lifting volume, leg press lifting volume or WAC sprint performance.(Continued on next page)

* Correspondence: [email protected] & Sport Nutrition Lab, Department of Health & Kinesiology, TexasA&M University, College Station, TX 77843-4243, USAFull list of author information is available at the end of the article

© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Jung et al. Journal of the International Society of Sports Nutrition (2017) 14:3 DOI 10.1186/s12970-016-0159-2

http://crossmark.crossref.org/dialog/?doi=10.1186/s12970-016-0159-2&domain=pdfmailto:[email protected]://creativecommons.org/licenses/by/4.0/http://creativecommons.org/publicdomain/zero/1.0/

(Continued from previous page)

Conclusions: Within the confines of this study, ingestion of PWS and/or PWS + S prior to exercise appears to bewell-tolerated when consumed by young, healthy individuals. The primary effects appear to be to increase REEresponses and improve perceptions about readiness to perform and cognitive function with limited to no effectson muscular endurance and WAC. The addition of 20 mg of p-synephrine to the PWS provided limited to noadditive benefits.

Trial registration: This trial (NCT02952014) was retrospectively registered on September 13th 2016.

Keywords: Ergogenic Aids, Dietary Supplement, Energy Drinks

BackgroundResearch has shown that ingestion of some ergogenicnutrients and/or caffeinated beverages prior to exercisecan improve mental focus and/or exercise capacity [1, 2].For this reason, a number of energy drinks and pre-workout supplements (PWS) have been developed andmarketed to active individuals. The primary ergogenicproperties in most of these supplements appears to bewater, carbohydrate, and caffeine [1]. However, morerecently PWS’s have been developed that not only containnutrients that may affect acute exercise performance (e.g.,carbohydrate, caffeine, nitrates, etc.) but also nutrientsthat can increase energy expenditure, reduce catabolism,and/or promote protein synthesis (e.g., amino acids, creat-ine, β-alanine, etc.) [1–3]. Theoretically, use of PWS’sprior to exercise may enhance mental focus, cognitivefunction, and/or exercise capacity and regular use ofPWS’s during training may lead to greater training adapta-tions. Consequently, there has been increased interest inexamining the acute and chronic safety and efficacy ofPWS’s marketed to active individuals as well as whetheradding potentially ergogenic nutrients to PWS’s maypromote additive benefits [1].This study examined the safety and efficacy of acute

ingestion of a market leading PWS on ratings of percep-tion of readiness to perform, resting energy expenditureand metabolism, cognitive function, exercise perform-ance, and markers of safety. The PWS studied containedseveral nutrients at previously reported effective dosesthat have ergogenic properties including caffeine [4],beta-alanine [5], creatine [6], nitrate [7, 8], argininealpha-ketoglutarate [9] as well as other nutrients pur-ported to effect cognitive function like tyrosine [10, 11]and Mucuna pruriens containing L-Dopa [12, 13]. It iswell established that consuming caffeine prior to exer-cise (e.g., 3–6 mg/kg) can improve exercise performance,cognitive function, and vigilance [1, 4]. A number ofstudies also indicate that ingestion of nitrate prior toexercise (e.g., 300 mg) can improve exercise capacity[7, 8, 14–17]. Theoretically, ingesting these nutrients ateffective doses in PWS’s prior to exercise may improveperceptions of readiness to perform, cognitive function,and/or exercise performance leading to higher quality

workouts. If so, regular use of these types of PWS mayeffect quality of training and/or training adaptationsparticularly if they contain nutrients that have beenreported to enhance training adaptations like beta-alanine [5, 18–24] and/or creatine [6, 25].Citrus aurantium is found in the peel of bitter orange

and contains p-synephrine which is a protoalkaloid withsympathomimetic properties [26–28]. Citrus aurantium(generally containing 20–100 mg of p-synephrine) hasbeen purported to serve as a mild central nervous systemstimulant [26, 28], suppress appetite [29], increase restingenergy expenditure and affect carbohydrate and fatoxidation rates [30–33], and promote weight loss [34–36]with no negative effects on the cardiovascular system[37–39]. There is also evidence that Citrus aurantiumingestion can effect memory [40, 41] and resistance-exercise performance [30]. Theoretically, adding Citrusaurantium to a PWS may promote greater resting energyexpenditure, cognitive function, and/or exercise capacityduring an exercise bout. The purpose of this study was toexamine the safety and efficacy of ingesting a marketleading PWS with and without p-synephrine on ratings ofperception of readiness to perform, cognitive function,resting energy expenditure and metabolism, exerciseperformance, and markers of safety. This paper presentsresults from a study evaluating the acute effects of PWSingestion with and without p-synephrine while the effectsof ingesting these PWS on training adaptations arepresented in a companion paper.

MethodsResearch designThis study was conducted in a randomized, doubleblind, counter-balanced, and crossover manner. Subjectsparticipated in a familiarization session and threetreatment testing sessions with a 1-week washout periodobserved between each testing session. The study wasconducted at the Exercise & Sport Nutrition Laboratory(ESNL) at Texas A&M University after obtainingapproval from the university ethics committee. Thefollowing description of methods and procedures pro-vides an overview of the study.

Jung et al. Journal of the International Society of Sports Nutrition (2017) 14:3 Page 2 of 15

https://clinicaltrials.gov/ct2/show/NCT02952014

Participant recruitment and familiarizationParticipants were recruited to participate in this studyfrom local advertisements. Inclusion criteria requiredthat each participant have at least 6 months of resistancetraining experience immediately prior to entering thestudy inclusive of performing bench press and leg pressor squat exercises. Participants were excluded if theynoted a history of treatment for metabolic disease,hypertension, thyroid disease, arrhythmias, cardiovascu-lar disease; and/or, if they were currently using anyprescription medication. Further exclusion criteria alsoincluded an intolerance to caffeine and/or other naturalstimulants; pregnant or lactating women; a history ofsmoking; and, excessive alcohol consumption (>12drinks/wk).Figure 1 presents a CONSORT schematic of enroll-

ment and treatment allocation to the study. A total of69 individuals responded to advertisements. Of these, atotal of 42 individuals met initial study entry criteria viaphone interview and were invited to a familiarizationsession where the details of the study were explained,

informed consent was obtained in compliance with ourInstitutional Review Board, medical history was assessed,and a general medical exam was performed. Height,weight, and body composition was determined. Partici-pants then had one repetition maximum (1 RM) benchpress and 1RM leg press determined. Participants alsopracticed the anaerobic sprint test used in the study. Atotal of 26 individuals began the study. One participantwithdrew due to not feeling comfortable with donatingblood samples after the first testing session. A totalof 25 individuals participated in the study.

Testing sequenceFigure 2 shows the timeline of testing procedures. Priorto each testing session, participants were instructed torefrain from exercise, caffeine, and supplements and/ormedications containing stimulants for 48 h prior to test-ing. Participants were asked to present to the lab after a12 h fast. Once arriving to the lab, participants donated~ 20 ml of blood via venipuncture of an antecubital veinusing standard procedures. Following blood sampling,

Fig. 1 CONSORT schematic of enrollment and treatment allocation to the study


participants completed a readiness to perform (RTP) visualanalogue scale (VAS) and completed a Stroop Color-Wordcognitive function test. Participants were then placed on anexam table in the supine position while electrodes wereplaced on the participant. The metabolic cart was then cali-brated. After at least 10 min of rest in the supine position;resting heart rate, blood pressure, and 12 lead electrocar-diographs (ECG) were obtained. Following this procedure,resting energy expenditure (REE) measurements were ob-tained for 10 min.Participants were then randomly given in a counterba-

lanced and double-blinded manner either one serving(12 g) of a flavored maltodextrin placebo (PLA); a PWScontaining β-alanine (3 g), creatine nitrate as a salt (2 g),arginine alpha-ketoglutarate (2 g), N-Acetyl-L-Tyrosine(300 mg), caffeine (284 mg), Mucuna pruiriens extractstandardized for 15% L-Dopa (15 mg), Vitamin C as As-corbic Acid (500 mg), niacin (60 mg), folate as folic acid(50 mg), and Vitamin B12 as Methylcobalamin (70 mg)with the remainder of the supplement consisting offlavored maltodextrin to equal 12 g (Nutrabolt Inc.,Brayan, TX); or, (3) the PWS with Citrus aurantium(PWS + S) extract standardized for 30% p-synephrine(20 mg) (Nutratech Inc., Caldwell, NJ). Supplementswere independently packaged by an independent thirdparty into coded single foil packets for double-blindadministration following Good Manufacturing Practicesand certified to contain the aforementioned ingredientsby VMI Nutrition (Salt Lake City, UT). The contents ofthe supplement packets were mixed into approximately235 ml of water.After the participant ingested the supplement; supine

heart rate, blood pressure, and ECG’s were obtainedevery 10-min during a 30-min REE test. Following REEassessment and approximately 1 h after ingestion of the

supplements, participants donated a post-supplementation/ pre-exercise blood sample and had RTP-VAS and Stroopcognitive function determined. Participants then performeda 2 min warm up followed by performing 3 sets of 10 repe-titions at 70% of 1 RM on the bench press interspersed by2 min rest between sets. During the third set, participantswere asked to complete as many repetitions as possible tofailure. Participants then rested for 5 min, warmed up for2 min, and then performed 2 sets of 10 repetitions and 1set to failure at 70% of 1RM on the leg press following simi-lar procedures. Following a 5 min recovery, participantsthen performed a 30 s WAC on a cycle ergometer. Partici-pants then had post-exercise RTP-VAS and Stroop cogni-tive function determined and donated a final blood sample2 h after ingestion of the supplements. The experiment wasrepeated using the alternate supplement administered in acounterbalanced manner two additional times following a1 week washout after each additional testing session.

ProceduresBody compositionBody mass and height were determined according tostandard procedures using a Healthometer Professional500KL (Pelstar LLC, Alsip, IL, USA) self-calibratingdigital scale with an accuracy of ± 0.02 kg. Whole bodycomposition measures (excluding cranium) were deter-mined with a Hologic Discovery W Dual-Energy X-rayAbsorptiometer (DEXA; Hologic Inc., Waltham, MA,USA) equipped with APEX Software (APEX CorporationSoftware, Pittsburg, PA, USA) by using procedurespreviously described [42].

Muscular strength and enduranceBench press tests were performed using a standardisotonic Olympic bench press (Nebula Fitness, Versailles,

Fig. 2 Study timeline


OH) while leg press was determined using a hip/leg sled(Nebula Fitness, Versailles, OH) using standard proce-dures [43]. Bench press and leg press 1RM’s were deter-mined during the familiarization session by having theparticipants follow a standard warm-up consisting of 10repetitions using 50% of their estimated 1RM, 5 repeti-tions using 70% of their estimated 1RM, and 1 repetitionusing 90% of their estimated 1RM. Participants weregiven 2 min recovery between attempts and performed1RM lifts until reaching a failure weight. After 5 min re-covery, participants warmed-up in a similar fashion asdescribed above and then performed 1RM lift attemptson a standard hip sled/leg press (Nebula Fitness, Ver-sailles, OH) according to standard procedures [43]. For 1RM determination, strong verbal encouragement wasprovided. Hand, seat, and foot placement positions wererecorded to standardize positions among testing ses-sions. During the muscular endurance test, participantswere asked to perform 2 sets of 10 repetitions at 70% of1RM, if possible, with 2-min rest between sets. Duringthe final set, participants were asked to complete asmany repetitions as possible until failure. Total liftingvolume was calculated by multiplying the amount ofweight lifted times the number of successful repetitionscompleted during each set. Day to day test reliability ofperforming this endurance test in our lab on resistance-trained participants has yielded a standard error ofmeasurement (SEM) of 92 kg, a SEM as a percent ofgrand mean of 4.1%, a CV of 0.34, and an intraclass cor-relation coefficient of 0.99 for 3 sets of bench press totallifting volume; and, a SEM of 820 kg, an SEM as a per-cent of grand mean of 6.4%, a CV of 0.32, and an intra-class correlation coefficient of 0.96 for 3 sets of leg presstotal lifting volume.

Cardiovascular markersHeart rate was determined by palpation of the radial ar-tery while blood pressure was determined using standardauscultatory procedures [44]. Resting 12-lead ECG’swere obtained using a Nasiff Cardio Card electrocardio-graph (Nasiff Associates, Inc, Central Square, NY, USA).

Resting energy expenditureREE assessments were conducted according to standardprotocols using a metabolic cart (Parvo Medics TrueMax2400 Metabolic Measurement System, ParvoMedics, Inc,Sandy, UT, USA). This test was conducted in a fastedstate with the participants lying supine on an exam table.A clear metabolic canopy was placed over the partici-pant’s head and neck, so that resting ventilation, oxygenuptake (VO2), and carbon dioxide (VCO2) measure-ments could be determined. The participants remainedmotionless without falling asleep for approximately10 min before supplementation and then about 30 min

after supplementation. Metabolic measurements wererecorded every minute over the testing period.

Readiness to perform assessmentRatings of perceptions of readiness to perform wereassessed using a visual analogue scale using a 5-item de-scriptive scale (strongly disagree, disagree, neutral, agree,strongly agree) arranged on a 20 cm dotted bar withthese terms equidistant along the scale. Participants wereasked to respond to the following statements: “I amlooking forward to today’s workout”; “I am optimisticabout my future performance”; “I feel vigorous and ener-getic”; and, “I have little muscle soreness” by circling thenumber or dot between numbers that best describedtheir current perceptions related to these questions. Dayto day test reliability of administering this test in our labhas yielded SEM’s of 0.35, 0.25, 0.28, 0.72; SEM as a per-cent of grand mean of 9.6%, 7.1%, 8.6%, 20.9%; CV’s of0.23, 0.19, 0.26, and 0.34; and intraclass correlation coef-ficients of 0.83, 0.86, 0.89, and 0.63 for questions 1through 4, respectively.

Cognitive function assessmentCognitive function was assessed using the Stroop Word-Color test [45, 46] which has widely-used and validatedin a variety of populations [46–50]. The test consists ofthree separate pages / tests with 100 items, presented in5 columns of 20 items. Items on the first page (Word)are the color words RED, GREEN, and BLUE in blackink. On the second page (Color) the items are XXX’scolored in red, green, or blue ink. Items on the thirdpage (Word-Color) are the words RED, GREEN, andBLUE printed in red, green, or blue ink with the limita-tion that word and ink could not match. Participantswere given standardized instructions and asked to readaloud each word or color on each page as fast as theycould for 45-s on page/test. The number of correct re-sponses obtained during the time period is used to as-sess cognitive function. Day to day test reliability ofadministering this test in our lab has yielded a SEM’s of4.9, 9.1, and 10.4 counts; an SEM as a percent of grandmean of 4.3, 10.5 and 16.7%; CV’s of 0.14, 0.19, and 0.25;and, intraclass correlation coefficients of 0.90, 0.68, 0.57for Word, Color and Word-Color, respectively.

Anaerobic capacity testWingate anaerobic capacity sprint tests were performedon a Lode Excalibur Sport Ergometer (Lode ExcaliburSport Ergometer, Lode BV, Groningen, Netherlands) withwork rate set at of 7.5 J•kg−1•rev−1. Participants wereasked to pedal as fast as possible prior to application ofthe workload and sprint at an all-out maximal capacityfor 30 s. Day to day variability in performing Wingateanaerobic capacity tests in our laboratory yielded an


SEM of 53 W, an SEM as a percent of grand mean of8.9%, a CV 0.26, and an intraclass correlation coefficientof 0.89 for mean power.

Blood chemistry assessmentPlasma creatine was assayed prior to and after 1 and 2 hof supplementation as a general indicator of supplementbioavailability using calorimetric assay kits (Sigma-Al-drich, St. Louis, MO), Test-to-test variability of perform-ing these assays yielded a SE of 0.09, an SEM as apercent of grand mean of 6%, mean CV of ± 0.1, and anintraclass correlation coefficient of 0.99. Serum alkalinephosphatase (ALP), aspartate transaminase (AST), ala-nine transaminase (ALT), creatine kinase (CK), lactatedehydrogenase (LDH), blood urea nitrogen (BUN), cre-atinine, total cholesterol (CHL), high density lipoprotein[HDL-c], low density lipoprotein [LDL-c], triglycerides[TG]), and glucose were assayed using a Cobas c 111(Roche Diagnostics, Basel, Switzerland) prior to and fol-lowing 2 h after supplementation. This analyzer has beenknown to be highly valid and reliable in previously pub-lished reports [51]. The internal quality control was per-formed using two levels of control fluids purchased fromthe manufacturer to calibrate to acceptable standard de-viations (SD’s) and CV’s. Samples were re-run if the ob-served values were outside control values and/or clinicalnorms according to standard procedures. Test-to-test re-liability (10-days) assessment yielded reliability CV’s ran-ging between 0.4 and 2.4% for low control samples and0.6–1.9% for high controls with precision ranging be-tween 0.8 and 2.4% on low and 0.5–1.7% for highcontrols.

Statistical analysisData were analyzed using general linear models (GLM)multivariate analysis of variance (MANOVA) with Wilks’Lambda and Greenhouse-Geisser adjustments usingSPSS version 22.0 software (IBM SPSS Statistics, Chi-cago, IL). When a significant treatment, time and/orinteraction alpha level was observed, Tukey’s least sig-nificant difference post-hoc analysis was performed todetermine where significance was obtained. Area underthe curve (AUC) was calculated on select variables usingGraphPad Prism 6 software (GraphPad Software, Inc.,La Jolla, CA). Delta values were calculated from sub-tracting baseline values with means and 95% ConfidenceInterval (CI) to determine whether changes from base-line and/or among treatments were significant [52].Means were considered significantly different when theprobability of error was 0.05 or less with statistical ten-dencies and effect size calculations noted when p-levelsranged between p > 0.05 to p < 0.10. All data are pre-sented as mean ± SD unless otherwise noted.

ResultsParticipant demographicsTable 1 presents participant demographics. A total of 25individuals completed the study (20 males and 5 fe-males). Participants were 22 ± 3 y, 176.1 ± 8.2 cm, 78.2 ±13.0 kg, 15.2 ± 5.2% fat, and 25.09 ± 3.0 kg/m2. No par-ticipant experienced an adverse medical event as resultof participation in this study that required medical treat-ment or any abnormal clinical findings that requiredmedical referral.

Cardiovascular markersTable 2 shows HR, systolic blood pressure (SBP), anddiastolic blood pressure (DBP) responses observedamong treatments. No significant treatment x time inter-actions were observed in HR, SBP, or DBP responses ob-tained prior to and during the REE test. Additionally, nonoticeable changes were observed in resting 12-leadECG recordings.

Resting energy expenditureFigure 3 presents oxygen uptake (VO2), carbon dioxideproduction (VCO2), and respiratory exchange ratio(RER) values (VCO2/VO2) observed during the post-supplementation REE test. MANOVA revealed an over-all significant Wilks’ Lambda treatments x time effect (p< 0.001) as well as significant univariate ANOVA treat-ments x time interactions VCO2 (p = 0.008) and RERvalues (p = 0.001). Post-hoc analysis revealed that PWSand PWS + S ingestion primarily effected VCO2 andRER responses compared to the PLA treatment and thatPWS ingestion promoted higher VCO2 and RER valuestoward the end of the 30 min REE test. Analysis of AUCchanges from baseline revealed significant differencesamong treatments in VO2 (PLA 684 ± 376; PWS 802 ±434; PWS + S 1,034 ± 584 ml/min, p = 0.015), VCO2(PLA 634 ± 262; PWS 1,151 ± 673; PWS + S 1,372 ±604 ml/min, p < 0.001), and RER (PLA 1.48 ± 0.67; PWS2.44 ± 0.98; PWS + S 2.79 ± 0.89, p < 0.001). Post-hocanalysis revealed that VO2 AUC in the PWS + S treat-ment was significantly greater than the PLA treatment(p = 0.013, CI [64, 636]) but not the PWS treatment.VCO2 and RER AUC values were significantly higher inthe PWS (VCO2 p < 0.001, CI [242, 792]; RER p < 0.001,CI [−.43, −1.53]) and PWS + S (VCO2 p < 0.001, CI[−1,036, −440]; RER p < 0.001, CI [−1.87, −0.78]) com-pared to the PLA treatment. However, no significantdifferences were observed between PWS and PWS + Streatments.

Perceptions of readiness to performPerceptions about readiness to perform are presented inTable 3. MANOVA revealed a significant overall Wilks’Lambda treatments x time interaction (p = 0.004) in


perceptions of readiness to perform questions. Signifi-cant univariate ANOVA treatments x time effects werealso observed in response to “I am optimistic about myfuture performance” and “I feel vigorous and energetic”.Post-hoc analysis revealed that participants in the PWSand PWS + S treatments rated optimism about perform-ance and feelings of vigor and energy higher than thePLA treatment after 1 h of ingestion. However, percep-tions about optimism about performance and vigor andenergy in the PWS + S treatment were lower than PLAand PWS responses after 2 h. No significant treatmentsx time interactions were seen in remaining questions.

Cognitive functionTable 4 presents Stroop Color-Word cognitive functionresults. An overall Wilk’s Lambda treatments x timeinteraction effect was observed among treatments (p <0.001). Significant univariate ANOVA treatment x timeinteractions were also observed in Word, Color andWord-Color scores. Post-hoc analysis revealed thatWord, Color and Word-Color scores significantly in-creased over time in the PWS and/or PWS + S treat-ments with values in the PWS and PWS + S treatmentssignificantly greater than the PLA at several data points.Figure 4 presents changes from baseline with 95% CIvalues. These graphs show that changes in Word, Color,and Word-Color were significantly increased abovebaseline (i.e., mean and 95% CI above baseline) more

consistently in the PWS and/or PWS + S treatmentscompared to the PLA treatment. Additionally, changesin the PWS and/or PWS + S were significantly greaterthan PLA responses at several data points. There wasalso some evidence that changes in the PWS + S treat-ment were significantly greater than the PWS treatmentat several data points. However, it should be noted thatpre-supplementation values in the PWS + S treatmentwere lower at baseline compared to PLA and PWS re-sponses so these data should be interpreted withcaution.

Performance assessmentTable 5 shows bench press and leg press lifting volumeobserved during the 3rd set to failure and for all threesets of exercise while Table 6 presents Wingate anaer-obic sprint capacity results. All participants completed10 repetitions during the first set. One of participantswas only able to complete 7 repetitions during the sec-ond set but this was consisted in each trial. MANOVArevealed tendencies toward significant differences amongtreatments in bench press 3rd set lifting volume (p =0.086, partial η2 = 0.08) and total lifting volume (p = 0.10,partial η2 = 0.08). Lifting volume for the 3rd set to failurealso tended to be greater in the PWS + S compared tothe PLA treatment (p = 0.057, partial η2 = 0.09, Cohen’sD = 0.18). No significant differences were observed in leg

Table 1 Participant Demographics

N Age Height BMI Body Weight Fat-Free Mass Body Fat

(y) (cm) (kg/m2) (kg) (kg) (%)

Overall 25 21.7 ± 3.0 176.1 ± 8.2 25.0 ± 3.0 78.2 ± 13.0 61.0 ± 11.6 15.2 ± 5.2

Male 20 21.4 ± 2.7 178.9 ± 5.9 25.9 ± 2.4 83.0 ± 8.5 65.5 ± 7.2 14.0 ± 4.8

Female 5 23.2 ± 3.1 164.8 ± 5.4 21.7 ± 2.4 59.3 ± 8.5 42.9 ± 5.9 20.1 ± 3.2

Data are means ± standard deviations

Table 2 Heart Rate and Blood Pressure Response

Variable Treatment Time (min) p-levelPre 0 10 20 30

HR (beats/min) PLA 58.2 ± 9.5 60.4 ± 8.1 58.6 ± 8.5 59.6 ± 8.3 60.6 ± 8.4 0.84

PWS 55.5 ± 7.3 58.2 ± 9.5 54.2 ± 7.2 56.5 ± 7.7 58.1 ± 8.1

PWS + S 56.6 ± 7.2 57.5 ± 8.8 56.5 ± 9.5 58.4 ± 9.1 60.4 ± 10.8

SBP (mmHg) PLA 113.3 ± 7.6 114.3 ± 8.0 112.7 ± 6.8 114.3 ± 6.3 113.6 ± 6.6 0.52

PWS 111.5 ± 7.1 112.4 ± 7.3 112.9 ± 8.6 112.8 ± 7.9 112.5 ± 8.2

PWS + S 113.1 ± 7.8 112.5 ± 8.3 113.0 ± 9.6 113.9 ± 10.6 114.6 ± 10.0

DBP (mmHg) PLA 69.6 ± 6.8 69.2 ± 6.5 68.8 ± 6.3 69.5 ± 7.4 69.1 ± 7.1 0.51

PWS 69.0 ± 6.7 70.7 ± 6.1 70.9 ± 7.1 70.6 ± 7.5 70.4 ± 7.7

PWS + S 69.6 ± 7.2 70.0 ± 6.7 71.0 ± 6.8 71.1 ± 8.1 68.4 ± 13.0

Data are means ± standard deviations for Heart Rate (HR), Systolic Blood Pressure (SBP), and Diastolic Blood Pressure (DBP). MANOVA analysis revealed overallWilks’ Lambda treatment (p = 0.28), time (p = 0.03), and treatment x time (p = 0.81). Greenhouse-Geisser univariate p-levels of interactions (treatment x time) arereported above


press or cycling sprint peak power, mean power, or totalwork.

Blood chemistryTable 7 presents plasma creatine values observed in re-sponse to supplementation treatments. Results revealedthat PWS and PWS + S ingestion significantly increasedplasma creatine levels after 1 h and 2 h in comparison tothe PLA treatment. Tables 8 and 9 present pre- and 2 hpost supplementation/exercise blood chemistry panels.No significant interactions were observed amongtreatments in ALP, ALT, AST, CK, or LDH. Significantinteractions were observed among treatments in BUN,creatinine, and BUN to creatinine ratio. As expected,PWS and PWS + S supplementation (which containedabout 1.3 g of creatine) resulted in a small increase increatinine in which values were well-within normallimits for active individuals [53, 54]. BUN and the BUNto creatinine ratio decreased indicative of less wholebody catabolism. No significant interactions were

observed among treatments in HDL-C, LDL-C or trigly-ceride levels. Significant treatments x time effects wereobserved in total cholesterol, the ratio of CHOL: HDLand blood glucose levels. However, given that partici-pants ingested caffeine with a small amount of malto-dextrin prior to exercise, these changes were expectedand within normal expected values for trained individ-uals undergoing intense exercise [53–56] as well aswithin normal clinical ranges [57].

DiscussionThe purpose of this study was to examine the effects ofacute ingestion of a PWS with and without p-synephrineon resting energy expenditure, perceptions of readinessto perform, cognitive function, and anaerobic exerciseperformance. Additionally, to examine the safety ofacute ingestion of these PWS’s on resting heart rate,blood pressure, 12-lead ECG tracings, and standardclinical blood chemistry panels. Results revealed thatingestion of these PWS’s did not promote clinically

Fig. 3 Oxygen update (Panel a), carbon dioxide production (Panel b), and respiratory exchange ratio values (Panel c) observed during the first30-min following supplementation. Data are mean ± SD. ^ represents p < 0.05 difference between PLA and PWS; + represents p < 0.05 differencebetween PLA and PWS + S; and, * represents p < 0.05 difference between PWS and PWS + S


significant changes in heart rate, blood pressure, ECGfindings, or clinical blood markers. Thus, acute ingestionof these PWS’s prior to exercise appeared to be well-tolerated when consumed by young, healthy individuals.The primary effect of ingesting these PWS’s prior to

exercise appeared to be an increase resting energy expend-iture, improved perceptions about readiness to perform,and improved cognitive function. There were limited to noeffects on bench press and leg press muscular endur-ance as well as anaerobic sprint capacity. Moreover,

Fig. 4 Changes in Stroop Word (Panel a), Color (Panel b), and Word-Color (Panel c) counts. Data are mean change and 95% CI. * representsp < 0.05 difference from baseline, a = p < 0.05 from PLA, b = p < 0.05 from PWS, c = p < 0.05 difference from PWS + S. † represents p > 0.05 top < 0.10 difference

Table 3 Readiness to Perform Visual Analogue Scale

Questions Treatment Time (h) p-level

Pre 1 2

I am looking forward to today’s workout PLA 3.67 ± 0.85 3.61 ± 1.00 3.61 ± 0.87 0.21

PWS 3.71 ± 0.77 3.89 ± 0.79 3.65 ± 0.65

PWS + S 3.71 ± 0.99 3.82 ± 1.17 3.51 ± 1.09

I am optimistic about my future performance PLA 3.74 ± 0.83 3.70 ± 0.94 3.78 ± 0.88 0.02q

PWS 3.88 ± 0.69 4.05 ± 0.73 a 3.83 ± 0.70

PWS + S 4.00 ± 0.69 4.21 ± 0.62 a 4.01 ± 0.71

I feel vigorous and energetic PLA 3.23 ± 0.95 3.35 ± 0.90 3.38 ± 1.04 0.001

PWS 3.19 ± 0.89 3.77 ± 0.78 *a 3.33 ± 1.09

PWS + S 3.33 ± 0.77 3.89 ± 0.73 *a 2.96 ± 0.97 a,b

I have little muscle soreness PLA 3.60 ± 0.99 3.42 ± 0.99 3.29 ± 1.01 0.17

PWS 3.54 ± 1.17 3.81 ± 1.35 3.25 ± 1.03

PWS + S 3.13 ± 1.31 3.27 ± 1.28 3.21 ± 1.12

Values are means ± standard deviations. MANOVA analysis revealed overall Wilks’ Lambda treatment (p = 0.03), time (p = 0.01), and treatment x time (p = 0.004).Greenhouse-Geisser linear or quadratic (q) univariate p-levels of interactions (treatment x time) are reported above * represents p < 0.05 difference from baseline.a denotes a significant difference from PLA. b denotes a significant difference from PWS. c denotes a significant difference from PWS + S


adding 20 mg of p-synephrine to the PWS providedlittle to no additive benefits. The following sectionsprovide a more detailed analysis of results observedand comparison to available literature.

Resting energy expenditureA number of studies have reported that ingestion ofenergy drinks and/or thermogenic type supplementsprimarily containing caffeine can increase resting metab-olism [58–65]. For example, Taylor and colleagues [65]reported that ingestion of caffeine enriched coffee(400 mg) increased REE by approximately 14% for up to3-h compared to consumption of coffee containingstandard amounts of caffeine (200 mg). Rudelle andcoworkers [66] reported that consuming beveragescontaining green tea catechins, caffeine, and calcium for

3-days increased energy expenditure by 106 ± 31 kcal/24 h. Ryan et al. [62] reported that ingestion of athermogenic supplement containing caffeine, capsaicin,bioperine, and niacin increased energy expenditure andoxygen update values. Wilborn and associates [64] re-ported that ingestion of a thermogenic supplementcontaining green tea extract and caffeine increased REEby 15-19% compared to 0.3–2.5% when ingesting aplacebo. Campbell and coworkers [60] reported thatingestion of a supplement containing 200 mg of caffeineand green tea extract significantly increased restingmetabolic rate from 7 to 9% for up to 3 h after ingestion.Moreover, Miles-Chan and colleagues [67] reported thatconsumption of a sugar free energy drink containing 120 mgof caffeine increased REE by about 4% and that the changesobserved were due to the caffeine in the drinks rather thanother nutrients (i.e., taurine and glucuronolactone).Citrus aurantium (generally containing 20–100 mg of

p-synephrine) has also been purported to increase rest-ing energy expenditure and/or effect carbohydrate andfat oxidation rates [30–33]. For example, Ratamass andcolleagues [31] reported that ingestion of 100 mg ofp-synephrine increased lipolysis primarily at rest as wellas post-exercise oxygen uptake, energy expenditure, andfat oxidation. Sale et al. [33] reported that ingesting asupplement containing 6 mg of p-synephrine, 150 mgcaffeine, and 150 mg catechin polyphenols increasedresting and exercise carbohydrate oxidation rates.Additionally, Gutiérrz-Hellín and Del Coso [32] reportedthat acute p-synephrine ingestion (3 mg/kg) increasedfat oxidation rates while exercising at low-to-moderateexercise intensities. Thus, there is support to the ration-ale that adding p-synephrine to a PWS can increasemetabolism and affect substrate utilization.Results of the present study provide some support to

this contention. In this regard, mean oxygen uptakeduring the 30 min REE test was increased by about 1.4%

Table 4 Stroop Word-Color Test

Variable Treatment Time (h) p-level

Pre 1 2

Word (counts) PLA 120.9 ± 15.7 121.1 ± 16.6 122.6 ± 18.0

in the PLA treatment compared to 5.6% in the PWStreatment and 8.6% in the PWS + S treatment. Therewas also evidence that PWS and PWS + S ingestionsignificantly increased resting VCO2 and RER to agreater degree than in the PLA treatment indicatinggreater carbohydrate oxidation. Analysis of AUCchanges from baseline indicated that while PWS had agreater impact on VO2 VCO2 and RER values; the PWS+ S observed greater changes from baseline compared tothe PLA treatment. These findings are consistent withseveral reports indicating that ingestion of thermogenictype supplements increases energy metabolism and/orcarbohydrate oxidation [33, 62, 66, 67] while contrastingother studies reporting either no effects [64] or greaterfat oxidation [32]. However, ingestion of PWS + Streatment did not result in higher mean VO2 values thanthe PWS treatment. Therefore, the addition of p-synephrine to the PWS did not promote greater overallenergy expenditure. Whether adding higher levels ofp-synephrine would promote added benefits remains tobe determined.

Perceptions of readiness to perform and cognitivefunctionNumerous studies indicate that ingesting caffeinecontaining energy drinks or supplements can improvemental focus and/or cognition [1, 4, 68–70]. There is

Table 6 Wingate Anaerobic Capacity Test

Variable Treatment Value p-level

Peak Power (Watt) PLA 1,578 ± 510 0.46

PWS 1,502 ± 561

PWS + S 1,491 ± 515

Mean Power (Watt) PLA 602 ± 131 0.61

PWS 595 ± 145

PWS + S 582 ± 188

Peak Power (Watt/kg) PLA 19.8 ± 5.1 0.51

PWS 19.0 ± 5.2

PWS + S 18.8 ± 5.2

Mean Power (Watt/kg) PLA 7.6 ± 1.0 0.78

PWS 7.6 ± 1.2

PWS + S 7.7 ± 1.3

Total Work (Joules) PLA 17,662 ± 4,605 0.49

PWS 17,850 ± 4,340

PWS + S 18,203 ± 4,658

Values are means ± standard deviations. MANOVA analysis revealed overallWilks’ Lambda group (p = 0.89). Greenhouse-Geisser univariate p-levels arereported above

Table 7 Plasma Creatine


0 1 2

Plasma Creatine PLA 0.74 ± 0.27 0.69 ± 0.21 0.71 ± 0.24

also evidence that Citrus aurantium ingestion can affectmemory [40, 41]. Therefore, it’s plausible that ingestionof a PWS containing caffeine and/or p-synephrine couldaffect mental focus and/or cognitive function prior toand/or during exercise. In the present study, participantsingesting the PWS’s indicated they felt more optimisticabout performance and more vigorous and energeticafter ingestion the PWS’s compared to the PLA treat-ment. Additionally, there was evidence that ingestion ofthe PWS and PWS + S consistently increased Word,Color, and Word-Color scores from baseline and thatsome of these changes were greater than PLA responsesafter 1 or 2 h. However, it should be noted that partici-pants started the PWS + S treatment with lower scoresprior to supplementation and the scores in the PWS + Streatment did not exceed PLA or PWS responses at anydata point so these results should be interpreted withcaution. Further, the addition of 20 mg of p-synephrineto the PWS supplement used in our study did not ap-pear to provide additive benefit. Results are in agreementwith Hoffman et al. [71] who reported a significantlygreater feeling of energy and focus compared to placeboafter ingesting a supplement containing a PWS but

contrast those of Gonzales and associates [72] who re-ported no significant difference in VAS ratings of energywhen ingesting a supplement containing caffeine, creat-ine, β-alanine. However, the participants in that studywere administered the supplement 10-min before per-forming resistance-exercise which may have limited re-sults since it takes about an hour for caffeine levels inthe blood to peak after caffeine ingestion [1, 4].

Exercise performanceNumerous studies have evaluated the effects of ingestingPWS’s and/or energy drinks containing a variety of nutri-ents on exercise performance [1]. For example, Walsh andcolleagues [70] reported that ingestion of a PWS contain-ing 2.05 g of an energy matrix (caffeine, taurine, glucuro-nolactone) with amino acids significantly improvedperceptions of energy, decreased perceptions of fatigue, animproved run time to exhaustion at 70% of VCO2 max.Gonzalez et al. [72] reported that acute ingestion of a pre-workout supplement containing caffeine, β-alanine, andcreatine significantly increased the number of repetitionsperformed at 80% of 1RM as well as peak and mean powerof bench press. Additionally, Ratamess et al. [30] reportedthat acute supplementation of PWS’s containing p-synephrine (100 mg), p-synephrine (100 mg) and caffeine(100 mg) increased the number of repetitions and liftingvolume (6 sets of squats for up to 10 repetitions at 80%1RM) compared to control and placebo treatments. Dif-ferences were more noted in the final 3 sets of exercise.Further, mean power and lifting velocity was reported tobe higher for the caffeine and p-synephrine treatmentcompared to control and placebo treatments. Conse-quently, there is evidence that ingestion of caffeine and/orp-synephrine prior to exercise may affect high intensityexercise performance.In the present study, no clear ergogenic benefit of PWS

or PWS+ S ingestion was observed. While participants inthe PWS+ S treatment tended to perform more total workduring the final set of bench press, no overall differenceswere observed in bench press or leg press lifting volume.Additionally, no differences were observed among treat-ments in the Wingate Anaerobic Capacity cycling sprinttest. Therefore, while participants reported they had moreenergy and were more optimistic about performance, itdid not result in statistically significant differences inupper and lower body muscular endurance or sprintcapacity. Whether adding more p-synephrine to the PWSor regular use of these PWS’s during training may yieldmore definitive ergogenic benefit remains to be unclear.

SafetyOne of the criticisms of use of energy drinks and/orPWS’s containing caffeine and/or p-synephrine is thatthey may increase heart, blood pressure, and/or prevalence

Table 9 Blood Lipid and Glucose Panel


0 2

Cholesterol PLA 170.6 ± 34.6 182.8 ± 35.1 0.006

(mg/dl) PWS 187.3 ± 46.6 a 180.2 ± 36.9

PWS + S 161.7 ± 29.8 a,b 174.0 ± 33.5 a

HDL-c PLA 54.9 ± 13.3 60.1 ± 16.0 0.57

(mg/dl) PWS 52.2 ± 13.9 58.9 ± 14.6

PWS + S 54.2 ± 16.2 60.1 ± 18.1

CHOL: HDL-c PLA 3.2 ± 0.9 b 3.2 ± 0.9 0.001

PWS 3.8 ± 1.3 a,c 3.2 ± 1.0 *

PWS + S 3.2 ± 1.0 b 3.1 ± 1.0

LDL-c PLA 104.3 ± 36.7 109.6 ± 41.2 0.55

(mg/dl) PWS 96.9 ± 31.9 104.5 ± 36.0

PWS + S 99.8 ± 41.2 104.6 ± 40.7

Triglycerides PLA 98.0 ± 58.6 89.3 ± 38.3 0.14

(mg/dl) PWS 109.5 ± 56.8 100.3 ± 47.5

PWS + S 88.3 ± 42.2 92.8 ± 54.6

Glucose PLA 90.2 ± 9.7 101.5 ± 14.4 * 0.03

(mg/dl) PWS 100.1 ± 16.0 a,c 114.4 ± 12.6 *a

PWS + S 90.4 ± 7.3 113.8 ± 15.0 *a

Values are means ± standard deviations for total cholesterol (CHOL), highdensity lipoproteins (HDL-c), the CHOL: HDL ratio (CHOL: HDL-c), low density li-poproteins (LDL-c), triglycerides and blood glucose. MANOVA analysis revealedoverall Wilks’ Lambda treatment (p < 0.001), time (p < 0.001), and treatment xtime (p < 0.001). Greenhouse-Geisser univariate p-levels of interaction (treat-ment x time) are reported above. * represents p < 0.05 difference from base-line. a denotes a significant difference from PLA. b denotes a significantdifference from PWS. c denotes a significant difference from PWS + S


of arrhythmias [1, 73, 74]. In the present study, acute inges-tion of PWS or PWS+ S did not significantly increasedheart rate, blood pressure, or effect resting ECG’s. Addition-ally, although there were some expected changes in bloodmarkers in response to exercise (hemoconcentration) and/or ingestion of maltodextrin, creatine, and caffeine contain-ing PWS’s (i.e., evidence of increased creatinine, lipolysis,and blood glucose release); values remained within normalexpected values for trained individuals undergoing intenseexercise [53–56] as well as within normal clinical ranges[57]. In this regard, creatinine levels expectedly increased toa greater degree in the PWS and PWS + S but these valueswere small and well-within normal ranges for active indi-viduals particularly when taking creatine [2, 6, 25, 53].Moreover, while significant interactions were observedamong treatments in BUN and the ratio of BUN: Creatin-ine, all values decreased suggesting less general whole bodycatabolism. Additionally, while significant differences wereseen in total cholesterol among treatments, total cholesteroldid not significantly change from baseline in any treatmentand the CHOL: HDL-c ratio either was unchanged ordecreased suggesting reduced risk. Finally, while differenceswere observed among treatments in pre- and post-exercise/supplementation blood glucose values and blood glucosewas higher with PWS ingestion suggesting greater hepaticglucose release (which would be beneficial during exercise);no significant differences were observed between PWS andPWS+ S treatments and all treatments and were withinnormal expected exercise ranges [57]. We also did notobserve any adverse events related to the study thatrequired medical treatment or clinical findings that re-quired medical referral. Consequently, ingestion of thesePWS’s prior to exercise did not appear to promote anyclinically relevant changes in these markers. These findingssupport prior reports that ingestion of PWS’s and/or energydrinks do not appear to pose undo health risk in apparentlyhealthy individuals [58, 59, 63, 75–78].

ConclusionWithin the limits of the present study, acute ingestion ofPWS and/or PWS + S prior to exercise appears to be well-tolerated when consumed by young, healthy individuals.The primary effects appear to be to increase resting energyexpenditure responses and improve perceptions aboutreadiness to perform and cognitive function with limited tono effects on muscular endurance and no effects on anaer-obic sprint capacity. The addition of 20 mg of p-synephrineto the PWS yielded limited to no additive benefits. Whetherregular use of the PWS’s used in this study and/or higheramounts of p-synephrine may promote greater benefitsremains to be determined. Given the widespread use ofPWS’s and energy drinks, additional study to examine thesafety and efficacy is warranted.

AcknowledgementsWe would like to thank the subjects that participated in this study as well asAbigail O’Connor, Chelsea Goodenough, Felix Ayadi, Chun-Hao Chang, JeremyCarter, and Sunday Simbo at the Exercise & Sport Nutrition Laboratory at TexasA&M University who assisted with data collection. We would also like to thankSteve Riechman, Chris Woodman, and Steve Smith for their insights on datainterpretation; Katherine Kelly and Cynthia Meininger for their valuable assistancein sample analysis; the Center for Translational Research in Aging and Longevityfor providing nursing support; and, Dr. JP Bramhall for providing medicaloversight.

FundingThis study was supported by Nutrabolt (Bryan, TX) through an unrestrictedresearch grant provided to Texas A&M University. The Director of ClinicalScience at Nutrabolt assisted in study design, data analysis and interpretation,and provided comments on the manuscript. However, the sponsor was notinvolved in data collection or data entry and there were no restrictions onpublication of the data or preparation of this paper. As stated above,competing interests were supervised and managed by a university approvedmanagement plan to insure that data were accurately reported.

Availability of data and materialsData and/or statistical analyses are available upon request on a case by casebasis for non-commercial scientific inquiry and/or educational use as long asIRB restrictions and research agreement terms are not violated.

Authors’ contributionsYPJ served as study coordinator and assisted with data collection, data analysis,and manuscript preparation. MK, EG, RD and DW assisted in data collection andsample analysis. CR serves as coordinator of the Exercise and Sport Nutrition Laband project manager. MG assisted in research design and consultation. PSMserved as study quality assurance manager. CPE served as a scientific liaison to thesponsor, assisted in study design, data analysis and interpretation, and providedcomments on the manuscript. However, CPE was not involved in data collectionor data entry and there were no restrictions on publication of the data orpreparation of this paper. RBK (corresponding author) obtained the grant, servedas study PI and assisted in the design of the study, data analysis, and manuscriptpreparation. All authors read and approved the final manuscript.

Competing interestsCP Earnest serves as a Director of Clinical Sciences for Nutrabolt and is a ResearchAssociate in the ESNL. RB Kreider serves as a university approved scientific advisorfor Nutrabolt. PS Murano serves as quality assurance supervisor in accordance toa conflict of interest management plan that was approved by the university’sresearch and compliance office, the internal review board, and office of grantsand contracts and monitored by research compliance. Remaining investigatorshave no competing interests to declare. The results from this study do notconstitute endorsement by the authors and/or the institution concerning thenutrients investigated.

Consent for publicationNot applicable.

Ethics approval and consent to participateThis study was reviewed and approved by Texas A&M University’sInstitutional Review Board (IRB2014-0022FX) in compliance in accordancewith the Declaration of Helsinki.

Author details1Exercise & Sport Nutrition Lab, Department of Health & Kinesiology, TexasA&M University, College Station, TX 77843-4243, USA. 2Nutrabolt, Bryan, TX77807, USA. 3Center for Translational Research in Aging and Longevity,Department of Health & Kinesiology, Texas A&M University, College Station,TX 77843-4243, USA. 4Institute for Obesity Research & Program Evaluation,Department of Nutrition and Food Sciences, Texas A&M University, CollegeStation, TX 77843, USA.

Received: 18 September 2015 Accepted: 16 December 2016


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AbstractBackgroundMethodsResultsConclusionsTrial registration

BackgroundMethodsResearch designParticipant recruitment and familiarizationTesting sequence

ProceduresBody compositionMuscular strength and enduranceCardiovascular markersResting energy expenditureReadiness to perform assessmentCognitive function assessmentAnaerobic capacity testBlood chemistry assessmentStatistical analysis

ResultsParticipant demographicsCardiovascular markersResting energy expenditurePerceptions of readiness to performCognitive functionPerformance assessmentBlood chemistry

DiscussionResting energy expenditurePerceptions of readiness to perform and cognitive functionExercise performanceSafety

ConclusionAcknowledgementsFundingAvailability of data and materialsAuthors’ contributionsCompeting interestsConsent for publicationEthics approval and consent to participateAuthor detailsReferences

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